The spectrum of activity of macrolides, including erythromycin, covers most relevant bacterial species responsible for upper and lower respiratory tract infections. 14-membered ring macrolides are well known for their overall efficacy, safety and lack of serious side effects. Erythromycin however is quickly degraded into inactive products in the acidic medium of the stomach resulting in low bioavailability and gastrointestinal side effects. Improvement of erythromycin pharmacokinetics has been achieved through the synthesis of more acid-stable derivatives, for example, roxithromycin, clarithromycin, and the 15-membered ring macrolide azithromycin. However, all these drugs, including 16-membered ring macrolides, present several drawbacks. They are inactive against MLSB-resistant streptococci (MLSB=Macrolides-Lincosamides-type B Streptogramines) and with the exception of azithromycin, weakly active against Haemophilus influenzae. Futhermore, the resistance of Streptococcus pneumoniae to erythromycin has increased significantly in recent years (5% to above 40%). There is a high percentage of cross-resistance to penicillin among these isolates, with a worldwide epidemic spread of 10-40% in some areas.
There is, therefore, a clear need for new macrolides that overcome the problem of pneumococcal resistance, have good pharmacokinetic properties and acid stability while continuing to be active against H. influenzae. These new macrolides will be ideal candidates for drug development in the first line therapy of upper respiratory tract infections (“URTI”) and lower respiratory tract infections (“LRTI”).
Kashimura et al. have disclosed 6-O-methylerythromycin derivatives having a tricyclic basic nuclear structure in European Application 559896, published Nov. 11, 1991. Also, Asaka et al. have disclosed 5-O-desoaminylerythronolide derivatives containing a tricyclic carbamate structure in PCT Application WO 93/21200, published Apr. 22, 1992.
Recently erythromycin derivatives containing a variety of substituents at the 6-O position have been disclosed in U.S. Pat. Nos. 5,866,549 and 6,075,011 as well as PCT Application WO 00/78773. Furthermore, Ma et al. have described erythromycin derivatives with aryl groups tethered to the C-6 position in J. Med. Chem., 44, pp 4137-4156 (2001). PCT application WO 97/10251, published Mar. 20, 1997, discloses intermediates useful for preparation of 6-O-methyl 3-descladinose erythromycin derivatives. U.S. Pat. Nos. 5,866,549 and 6,075,011, and PCT application WO 00/78773, published Dec. 28, 2000, disclose certain 6-O-substituted erythromycin derivatives.
PCT Application WO 03/095466 A1, published Nov. 20, 2003 and PCT Application WO 03/097659 A1, published Nov. 27, 2003 disclose a series of bicyclic erythromycin derivatives.